1. Field of the Invention
The invention relates to a device for protecting a microphone against external disturbances, such as electromagnetic interference and noise and quick changes of temperature, as well as moisture and dust.
2. Description of the Related Art
In the protection of microphones, a problem is found particularly in achieving effective protection against electromagnetic coupling by means of an arrangement which should be as small and simple as possible. Electro Magnetic Compatibility, EMC, is particularly important in a mobile station, because a mobile station can be used in very variable and demanding environments.
There is a prior art device for protecting microphones from disturbances which consists of a metal screen or a plastic screen coated with metal, such as copper. When the microphone to be protected is small, the protecting device must consist of a very small piece of screen, which is difficult to handle in an industrial production process. Installing the piece of screen together with the microphone in the apparatus requires great accuracy and is thus demanding work. The success of the protection is in this case dependent on the joints between the protective frame of the microphone and the protective screen, and the results can vary if the protective screen cannot be installed accurately enough.
Using a protective screen to protect a microphone from disturbances does not provide protection against quick changes of temperature. Protection against noise conducted via the casing and frame of the apparatus is also needed.
In another prior art method, the microphone is placed deep inside the apparatus so that the air passage becomes long. Thus the electrostatic disturbances cannot break the microphone. This solution requires a lot of space in the apparatus and affects the sound quality.
The purpose of the present invention is to create a solution for protecting the microphone against external disturbances, in which solution the above mentioned drawbacks of the prior art can be avoided.